A hand-held pneumatic hammer drill comprises a pneumatic percussion mechanism, which is driven by a motor. A pneumatic chamber forms an air spring, which couples a percussion means to an exciter that is moved by the motor. The percussion mechanism is deactivated when the user does not apply any contact pressure to the tool in order to protect the percussion mechanism against excessive loading. As soon as the user presses the hammer drill against the tool, the percussion mechanism starts to work again. In high-powered machines, it has proven difficult to control the guidance of the hammer drill when pressing it against the tool again.